Method and apparatus for controlling the ratio of gases in a mixture

ABSTRACT

A method and apparatus for controlling the ratio by weight of at least a first and a second gas in a mixture. The first gas is separated into first and second parts. The first part of the first gas is mixed with the second gas, and that mixture is compared with the second part of the first gas as a function of their respective molecular weights and independently of their temperature. The percentage by weight of the second gas mixed with the first part of the first gas is adjusted to its desired value in response to the comparison of the second part of the first gas with the mixture of the first part of the first gas and the second gas. The separated gases are then mixed together to obtain the controlled percentages by weight of the first and second gases.

United States Patent [191 Boothe 1 Oct. '29, 1974 METHOD AND APPARATUS FOR CONTROLLING THE RATIO OF GASES IN A MIXTURE [75] Inventor: Willis Anson Boothe, Scotia, N.Y. [73] Assignee: General Electric Company, New

[58] Field of Search 137/3, 7, 88, 89, 90, 110; 261/69 R, DIG. 69

[56] References Cited UNITED STATES PATENTS 3,348,562 10/1967 Ogren 137/806 3,672,339 6/1972 Lazar 26l/DlG 69 3,762,428 10/1973 Beck 137/88 Primary Examiner-Alan Cohan Attorney, Agent, or Firm-S. A. Young; P. L. Schlamp; R. G. Simkins [57] ABSTRACT A method and apparatus for controlling the ratio by weight of at least a first and a second gas in a mixture. The first gas is separated into first and second parts. The first part of the first gas is mixed with the second gas, and that mixture is compared with the second part of the first gas as a function of their respective molecular weights and independently of their temperature. The percentage by weight of the second gas mixed with the first part of the first gas is adjusted to its desired value in response to the comparison of the second part of the first gas with the mixture of the first part of the first gas and the second gas. The separated gases are then mixed together to obtain the controlled percentages by weight of the first and second gases.

14 Claims, 4 Drawing Figures METHOD AND APPARATUS FOR CONTROLLING THE RATIO OF GASES IN A MIXTURE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for controlling the ratio of gases within a mixture.

2. Description of the Prior Art Quite often, it is necessary to accurately control the percentages or ratios of the constituents of a gaseous mixture. Such is particularly the case when the gaseous mixture is comprised of a combustible component and another component which supports combustion. More specifically, when the combustible component is vaporized fuel, such as gasoline, and the component supporting combustion is air, it has been found to be difficult to accurately control the fuel to air ratio by weight of the mixture within the range of, for example, l to 2 percent. Such accurate control is becoming increasingly necessary as efforts to curtail pollution of the environment increase, regardless of whether the combustible gas mixture is to be fed into an internal combustion engine, a heat engine, a boiler or a furnace.

One difficulty encountered in controlling the constituents of gas mixtures containing a combustible constituent is caused by the fact that the combustible constituent constitutes a relatively small overall percentage by weight of the gaseous mixture. For example the fuel to air ratio for an internal combustion engine is often 1 to 14. Under these circumstances it is quite difficult to accurately control the fuel to air ratio by weight when the vaporized gasoline, which is mixed with the air within a carburetor, is such a small percentage by weight of the overall combustible mixture. A further problem encountered in attempting to accurately control the gaseous constituents relates to the fact that various characteristics of these gaseous constituents are dependent on and change in accordance with corresponding changes in temperature.

OBJECTS OF THE INVENTION It is therefore an object of this invention to provide an improved method and apparatus for controlling the percentages by weight of the constituents in a gaseous mixture.

It is another object of this invention to provide an improved method and apparatus for controlling the fuel to air ratio by weight of a combustible gaseous mixture for heat engines, boilers, furnaces and internal combustion engines.

It is another object of this invention to provide a flu- 'idic carburetor for internal combustion engines which more accurately controls the fuel to air ratio by weight of the vaporized mixture which is fed into the internal combustion engine.

It is another object of this invention to provide an improved method and apparatus for controlling the fuel to air ratio of a combustible gaseous mixture which is dependent on the molecular weight of the gaseous constituents and independent of temperature.

These and other objects of the invention will be pointed out in and understood from the following.

SUMMARY OF THE INVENTION In accordance with a broad aspect of the invention there is provided an improved method and apparatus for controlling the percentages by weight of at least a first and a second gas in a mixture. The first gas is separated by first and second flow paths into first and second predetermined parts flowing within the respective first and second flow paths. The first part of the first gas is mixed with a second gas within the first flow path.

Representative portions of the gases are obtained from the flow paths, and the second part of the first gas is compared with the mixture of the first part of the first gas and the second gas as a function of their respective molecular weight, while the representative portions of the gaseous constituents are passed through a heat exchanger so that both gaseous portions are at the same temperature.

In one embodiment, the temperature of the gaseous constituents is constant, while the representative portions are fed to respective first and second oscillators after passing through the heat exchanger. Output signals are generated from the oscillators at respective first and second frequencies which are a function of the variation in the molecular weight of the representative portions of the gaseous constituents. The output signals from the oscillators are combined in a beat detector to obtain the difference between the first and second frequencies. This detected signal is converted to an analog signal proportional to the difference in the first and second frequencies. The converted analog signal is compared with a reference signal in a comparator amplifier, wherein variations in the desired percentages by weight of the gases are made by varying the reference signal. The output signal from the comparator amplifier controls a gas meter control device which increases or decreases the quantity by weight of the second gas mixed with the first part of the first gas. The second part of the first gas is mixed with the mixture of the first part of the first gas and the second gas to obtain the controlled mixture.

In another embodiment of the invention, the temperatures of the gases flowing into the first and second flow paths may vary, but the system is still made independent of temperature, since the first and second'oscillators are so designed that their output frequencies for the desired percentages of the first and second gases are equal.

In a third embodiment of the invention, a fluidic carburetor is provided for feeding vaporized fuel and air ata desired fuel to-air-ratio to an internal combustion engine. The fuel to air ratio is made variable by using a variable volume resonator cavity to establish the reference frequency. The volume of the resonator cavity is varied by a piston or bellows which is movable in response to changing conditions of the engine, such as changes in manifold vacuum and low temperature override.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic flow and block diagram of one embodiment of the invention for controlling the percentages by weight of the gases in a mixture for a system in which the temperature of the gases are constant;

FIG. 2 is a schematic flow and block diagram of another embodiment of the invention for controlling the percentages by weight of the gases in a mixture wherein the temperature of the gaseous components can change without affecting the operation of the system;

FIG. 3 is a schematic flow and block diagram of another embodiment of the invention for controlling the percentages by weight of the gases in a mixture, and more particularly for controlling the fuel-to-air ratio of a mixture of vaporized fuel and air flowing through a fluidic carburetor of an internal combustion engine; and

FIG. 4 is a partial schematic diagram of the embodiment shown in H6. 3 wherein the gases flowing from the heat exchanger to the resonator cavity and the fluidic generator are reversed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, one embodiment of the invention will now be described.

A first gas is fed through a first chamber in the direction of arrow 12. Although this first gas need not be limited to any specific gas, in this and the following embodiments, this gas will be considered to be one that will support combustion, such as air. The air continues to flow in the dirction of arrow 12 through chamber 10 and is separated into first and second respective flow paths 14 and 16. The orifices of respective flow paths l4 and 16 are specifically dimensioned to insure that predetermined percentages by weight of air flow through each of the flow paths. in this example, while 50 percent by weight of the air flows through each flow path, it should be understood that such percentages are given by way of example only and the scope of the invention is in no way limited thereby. A second gas is fed through a valve 18, via a suitable fluidic conduit 20, and into flow path 14 so that a portion of the first gas and the second gas are mixed therein. While the second gas need not be restricted to any specific gas, in this example, the second gas will be considered to be a combustible gas, such as a gaseous fuel, a vaporized liquid fuel or an atomized fuel which is vaporized upon being mixed with the first part of the air.

A representative portion by weight of the mixture of the first part of the air and the second gas from within the first flow path 14 is fluidically coupled to a heat exchanger 22, via a fluid conduit 24. Similarly, a representative portion by weight of the second part of the air from within second flow path 16 flows to heat exchanger 22, via a second fluid conduit 26. Heat exchanger 22 can be a thin wall, low thermal mass having thin plates and multiple passages for quickly equalizing the temperatures between the representative portions of the second part of the air and the mixture of the first part of the air and the second gas.

After the representative portions of the gases exit the heat exchanger at the same temperature, the representative portion of the second part of the air if fluidically coupled to the input ofa fluidic oscillator 28, via a fluid conduit 30, and the representative portion of the mixture of the first part of the air and the second gas is fluidically coupled to another fluidic oscillator 32, via a fluid conduit 34. A satisfactory form of fluidic oscillator is described in US. Pat. No. 3,618,385, inventors L. R. Kelley, et al, entitled Fluidic Temperature Sensor," issued Nov. 9, 1971 and assigned to the same assignee as the assignee of the present invention. In this type of oscillator, an output signal is produced having a frequency which is proportional to the acoustical velocity of the gas being sensed, wherein the acoustical velocity is a function of the molecular weight and temperature of the gas. Since, in the system shown in FIG. 1, the temperatures of the gaseous constituents prior to entering the heat exchanger are required to be constant, first and second output fluidic signals from re spective oscillators 28 and 32 are generated at respective first and second frequencies (F, and F which frequencies are inversely proportional to the square roots of the respective molecular weights of the second part of the air, and the mixture of the first part of the air and the second gas.

The first and second output signals from respective oscillators 28 and 32 are fluidically coupled to a beat detector 36, which produces an output signal at the difference frequency (F, F between the first and second signals fed thereinto. The beat detector can typically be comprised of a summing amplifier and a fluidic beam deflector rectifier. The output signal from beat detector 36 is fluidically coupled to a frequency to analog detector 38. The analog output from detector 38 is a fluidic signal whose pressure (Fe) is proportional to the difference frequency (F, F of the input signal thereto. A typical example of suitable fluidic circuits for beat detector 36 and frequency to analog detector 38 have been described in a lecture to the Advisory Group for Aerospace Research and Development on September 1969 by W. A. Boothe, entitled Fluidic Signal Processing Techniques for Aerospace Control Systems" and published in Agardograph-l35 as part of lecture series XXXV, pages 3-1 to 3-22.

Analog signal (Fe) is fluidically coupled to an input port 40 of a comparator amplifier 42, and a reference pressure signal (Pr) is fluidically coupled to a control port 44 of comparator amplifier 42. An output pressure signal (P0) is produced by comparator amplifier 42, which signal is proportional to the comparison of analog signal (Pe) with reference pressure signal Pr. A suitable configuration for comparator amplifier 42 and its operation are described in US. Pat. No. 3,534,755, inventor Thomas F. Urbanowsky, entitled High Signal To Noise Fluidic Amplifier And Fluidic Components, issued Oct. 20, 1970 and assigned to the same assignee as the assignee of the present invention. Output pressure signal (Po) from comparator amplifier 42 is fluidically coupled to a gas meter control device 46, which can be a spring biased diaphragm actuator. Valve 18 can be a needle valve which is stroked by the diaphragm actuator, to control the feed of the second gas or vaporized fuel into flow path 14.

Flow paths l4 and 16 converge into a down stream chamber 48 in order to achieve the desired percentages (fuel to air ratio) by weight for the total mixture of the air and the second gas (fuel), which, in this example, continues to flow into a combustor in a heat engine, boiler, furnace, etc. In operation, the setting of the percentages by weight of the gas mixture is determined by varying the reference pressure to control port 44 of comparator amplifier 42 until the desired fuel-to-air ratio is obtained.

Control and adjustment of the fuel-to-air ratio by weight will now be more specifically described. As previously described, the air flow is separated into a first and a second part by weight. Vaporized fuel is mixed with the first part of the air. The temperature of both this mixture and the second part of the air are made equal with respect to one another. The second part of the air is then used to generate a reference signal at a first frequency (F,) which is inversely proportional to the square root of the molecular weight of the second part of the air, while the mixture of the first part of the air and the vaporized fuel is used to produce a second signal at a second frequency which is inversely proportional to the square root of the molecular weight of the mixture. The first and second signals are combined to produce a difference frequency (F, F which is then converted to an analog pressure signal (Pe) which is proportional to the difference frequency. This analog signal (Pe) is compared with a reference pressure signal (Pr) to produce an output pressure signal (Po) which controls and adjusts the flow of the fuel to be mixed with the first part of the air flow. The reference pressure signal (Pr) is adjusted to set the desired fuelto-air ratio by weight. If the fuel mixture becomes either too rich or too lean, the frequency (F of the second signal changes, and as a consequence so does the difference frequency (F, F The change in the difference frequency causes a change in the analog pressure signal (Pe), which, in turn, causes a change in the output pressure signal (Po). This change in the output pressure signal then causes an adjustment in the fuel feed rate into flow path 14 so that the fuel-to-air ratio readjusts to its desired value.

In effect, the percentages by weight of the mixture of the fuel and the first part ofthe air is initially being controlled, while the second part of the air flow is initially being used to generate a reference signal at the first frequency (F,). Thus, while the total weight of air flow is much greater than the weight of fuel, control and adjustment of the fuel-to-air ratio is improved by initially mixing the fuel with only a portion of the air flow, in this instance 50 percent by weight. Furthermore, by decreasing the percentage by weight of the first part of the air which is initially mixed with the fuel flow, this mixture, in effect, is made to be more sensitive to the final air to fuel ratio, which in turn causes the difference frequency (F, F to be much greater. This, in turn, increases the sensitivity of the analog signal Fe, and the sensitivity of the control and adjustment of the final mixture of the air and fuel is thereby improved. However, as the percentage by weight of the first part of the air, which is initially mixed with the fuel, decreases, the temperature of the mixture of the first part of the air and the fuel begins to more closely approximate the actual temperature of the fuel, and thus the difference in temperature between this mixture and the second part of the air begins to increase. As this difference in temperature between the second part of the air and the mixture of the first part of the air and the fuel increases, the heat exchanger must become larger and more expensive in order to be sure that the temperature of the mixture of the first part of the air and the fuel is equal to the temperature of the second part of the air when these gaseous constituents exit the heat exchanger. Therefore, while the percentages of air flowing through flow paths l4 and I6 can vary widely, depending upon the required degree of sensitivity of control over the fuel-to-air ratio by weight, practical economic and physical design considerations for the heat exchanger actually may limit the minimum percentage of the first part of the air by weight which can flow through flow path 14 to, for example, approximately 25 percent by weight. The temperature of the air flowing through chamber 10 and the temperature of the fuel being fed into flow path 14 remains substantially constant in order to insure that the frequencies (F, and F of the respective first and second generated signals will be dependent solely on the molecular weight of their respective gaseous constituents and independent of temperature. While the control elements of the system shown in FIG. 1 are described as fluidic components, it should be understood that these elements could be replaced by electrically equivalent components. For example, oscillators 28 and 32 can be replaced by microphones coupled to organ pipes or other acoustic resonators for converting the acoustic velocity of the gases to electrical signals at specified frequencies, while detectors 36 and 38 and amplifier 42 can also be replaced by standard electrically equivalent circuits.

In FIG. 2 a second embodiment of the invention is described, wherein the temperature of the gaseous constituents entering the heat exchanger can vary, while the ratio of the gases, i.e., fuel to air ratio, by weight is held constant. In this embodiment, while the first and second signals at the respective first and second frequencies (F, and F are generated from oscillators 28 and 32, these signals are not combined in a beat detector to obtain the difference frequency as done in the embodiment shown in FIG. 1. Instead the first signal at the first frequency (F,) is converted by a first frequency to analog detector 50 to a first analog signal (P,) proportional to the first frequency (F and the second signal at the second frequency (F is converted by a second frequency to analog detector 51 to a second analog signal (P2) proportional to the second frequency (F Analog signals P,and P are then fed to inputs 44 and 40 of comparator amplifier 42 in the same manner as previously described with respect to the embodiment shown in FIG. 1 except that the reference pressure signal (Pr) is no longer applied to input 44.

The second embodiment is made independent of variations in the initial temperature of the air flow in chamber 10 and the fuel flowing into first flow path 14 by designing the characteristic lengths of oscillators 28 and 32 so that the first and second frequencies (F, and F of the first and second respective generated signals are made equal for the desired percentages by weight of the gaseous mixture. Thus, at the desired fuel-to-air ratio, F, equals F and P, equals P whereby the output analog signal P0 of amplifier 42 is set at a value which causes gas meter control 46 to stroke needle valve 18 to a position that allows the necessary percentage by weight of fuel to flow into flow path 14 to insure that the desired fuel to air ratio flows through downstream chamber 48. If there is a change in the temperature of either the air or the fuel flowing into the flow paths, the temperature of the gaseous constituents flowing out of the heat exchanger also changes even though the temperature of the gaseous constituents are still the same with respect to each other. This change in temperature of the gases flowing into oscillators 28 and 32 causes a corresponding and equal change in the first and second frequencies (F, and F,,) of the first and second generated signals from respective oscillators 28 and 32. This equal change in frequency also causes an equal change in each of analog pressure signals P, and P which changes are cancelled out and, the output signal (P0) of comparator amplifier 42 is not effected. Thus, the embodiment shown in FIG. 2 is effectively independent of variations in the temperature of the air and fuel flowing into the heat exchanger as long as these temperature variations are not so great that the heat exchanger can no longer insure that the gaseous constituents exiting therefrom are at the same temperature. If the difference in temperature between the air flowing into flow paths 14 and I6 and the gasoline flowing into flow path 14 is so great that the temperature of the separate gaseous constituents exiting the heat exchanger are not the same, then the percentage of air flowing through flow path 14 can be increased so that the temperature of the mixture in flow path 14 more closely approximates the temperature of the air flowing through flow path 16, thus reducing that difference in temperature and alleviating the burden on the heat exchanger.

In operation, if the flow of fuel into flow path 14 is in excess of the desired percentages, then the frequency F of the second signal generated by oscillator 32 will decrease accordingly, thus causing a corresponding decrease in analog signal P This decrease in analog signal P will cause output signal Po from comparator amplifier 42 to change in a first direction, which will cause a change in the setting of needle valve 18 and a concurrent reduction in the flow of fuel into flow path 14. Similarly, if the flow of fuel into flow path 14 becomes less than the desired amount, the molecular weight of the mixture flowing into fluidic oscillator 32 decreases and causes an increase in the second frequency (F generated by oscillator 32. This increase in the second frequency (F of the second signal generated by oscillator 32 causes a corresponding increase in the second analog signal (P The increase in analog signal P causes a corresponding change in a second direction of output signal Po from comparator amplifier 42, which, in turn, causes needle valve 18 to be readjusted to allow for an increase in the flow of fuel into flow path 14. In this embodiment, the generated first signal at the first frequency (F serves as the reference signal for the system.

The fluidic system shown in FIG. 3, which is basically similar to the system shown in FIGS. 1 and 2, has been modified to be suitable for use as a fluidic carburetor in an internal combustion engine by allowing the desired fuel-to-air ratio by weight to be varied in accordance with engine requirements, while the system remains relatively independent of variations in the temperature of the air and fuel being injected into the carburetor. The difference between the fluidic carburetor shown in FIG. 3 and the systemsshown in FIGS. 1 and 2 resides primarily in the control circuitry 52 positioned between the fluidic outputs of the heat exchanger 22 and the inputs to comparator amplifier 42. Additionally, the carburetor shown in FIG. 3 includes a standard air filter 54 positioned upstream of chamber 10, a throttle 56 positioned in downstream chamber 48 and a manifold vacuum line 58 which fluidically couples control circuitry 52 to the inlet manifold of the internal combustion engine via downstream chamber 48.

Included within control circuitry 52 is a fluidic oscillator 60 having first and second output ports 62 and 64, a first flow restrictor 66, a resonator cavity 68, a fluidic conduit 70, a piston 72, a second flow restrictor 74, a decoupler and amplifier 76, a phase discriminator 78, a third flow restrictor 80, and a phase shifter 82.

In operation, a respective portion of the second part of the air from the output of the heat exchanger is drawn into oscillator 60 by manifold vacuum 58. Oscillator 60 generates first and second output signals at a frequency Fo which exit from their respective output ports 62 and 64 in such a manner that the first signal is 180 out of phase with the second signal. The frequency (F0) of the output signals generated by fluidic oscillator 60 is a function of the molecular weight and temperature of the second part of the air flowing from the heat exchanger. Vacuum manifold 58 draws a representative portion of the mixture of the fuel (vaporized gasoline) and the first part of the air from the output of the heat exchanger into the interior of resonator cavity 68 via fluidic conduit 70. Resonator cavity 68 has a variable volume, wherein the volume is adjustable by movement of piston 72 therein or a bellows (not shown). Piston 72 may move in response to conditions of the internal combustion engine, such as low temperature override and/or changes in manifold vacuum. The resonant frequency of resonator cavity 68 is a function of the volume of the resonator cavity, and the molecular weight and temperature of the mixture of the fuel and the first part of the air which is fed therein. The second signal generated by oscillator 60 flows through the resonator cavity, and then through flow restrictor 74 and into decoupler and amplifier 76. Decoupler and amplifier 76 amplify the fluidic signal and produce push-pull output signals S1 and S2, which signals are 180 apart. S1 and S2 are coupled to the input of phase discriminator 78. In the interim, the first generated signal from output 62 of oscillator 60 is fed through flow restrictor 80, then through a delay or phase shifter 82 and then into another input of phase discriminator 78. The output of phase discriminator 78 produces, as before, analog pressure signals P and P which are fluidically coupled to comparator amplifier 42. From comparator amplifier 42 to flow path 14, the system operation is the same as that of the embodiments described in FIGS. 1 and 2. A further description of the components in control circuitry 52 and their operation is provided in U.S. Pat. No. 3,461,892, inventors W. A. Boothe, et al, and entitled Fluidic Controls Particularly For Turbine Engines, issued Aug. I9, 1969, and assigned to the same assignee as the assignee of the present invention.

For purposes of this discussion, the resonent frequency (Fr) of the resonator cavity serves as the refer ence frequency for the system. When frequency Fo of the second generated signal from oscillator 60 is equal to the resonant frequency of the resonator cavity, the phase of the second signal remains unchanged as it passes through the resonator cavity and to the input of decoupler and amplifier 76. When the percentage by weight of fuel being injected into flow path 14 increases, the resonant frequency (Fr) of resonator cavity 68 decreases so that frequency F0 is greater than the resonant frequency (Fr) of resonator cavity 68. Under these circumstances the phase of the second signal generated from oscillator 60 at flow restrictor 74 is lagging the phase of the same signal at flow restrictor 66. This, in turn, causes a shift in phase of signals S1 and S2 being compared to the phase of the first signal generated from oscillator 60 after it has been shifted in phase by 90. Under these circumstances, analog signals P and P at the input to comparator amplifier 42, adjust and cause a corresponding change in the output analog signal P0 of comparator amplifier 42. This, in turn, causes a decrease in the flow of fuel into flow path 14. The decrease in the flow of fuel into flow path 14 causes a corresponding drop in the molecular weight of the mixture which is fed into the resonator cavity,

thereby resulting in an increase in the resonant frequency (Fr) of the resonator cavity until Fr is equal to F0. Similarly. when the fuel fed into flow path 14 is too low, the drop in the molecular weight of the gaseous mixture within resonator cavity 68 causes an increase in the resonant frequency (Fr) of resonator cavity 68 so that the phase of the second signal generated by oscillator 60 at flow restrictor 74 is leading with respect to its phase at flow restrictor 66. Again similar corrective action is taken by the system to increase the flow of fuel to flow path 14, and thereby decrease the resonant frequency of the resonator cavity, until the resonant frequency of the resonator cavity equals the frequency (F) of the second signal generated by oscillator 60. At this point it should be noted that the system remains relatively independent of changes in temperature of the air and the fuel which is injected into the system, since F0 and Fr change equally in value with the corresponding changes in temperature. Similarly, changes in the desired fuel to air ratio by weight can be made by varying the volume of the resonator cavity by movement of piston 72 in response to demands of the internal combustion engine (i.e., manifold vacuum and/or low temperature override), which, in turn, will cause a shift in the feed of the fuel into flow path 14, until the resonant frequency (Fr) of the resonator cavity is again equal to F0.

As shown in FIG. 4, alternatively, the second part of the air from flow path 16 can be fed to resonator cavity 68, while the mixture of the first part of the air and the fuel can be fed to fluidic oscillator 60, which is just the reverse of the flow of the gaseous constituents shown in F IG. 3. Other than this, the operation of the embodiment shown in FIG. 4 is identical to that of the embodiment shown in FIG. 3. Again referring to H6. 3, it

should be understood that the first and second fluidic signals after passing through respective flow restrictors 80 and 74, can be converted to electrical signals using suitable acoustical microphones, while phase shifter 82, decoupler and amplifier 76, and phase discriminator 78 can again bereplaced with standard electrically equivalent elements.

In all of the embodiments described above, the fuel flow is modified by the control circuit in order to maintain a desired weight ratio of fuel flow to air flow, with air flow being the independent variable. It should also be noted that the above described embodiments can be modified so that the air flow can be adjusted by the control circuit to maintain the desired air to fuel ratio in cases where fuel flow is the independent variable. ln such a case, for example, referring to FIG. 3, the valve actuator 46 would position throttle valve 56 instead of the fuel needle valve 18.

Although the invention has been described with reference to specific embodiments thereof, numerous modifications are possible without departing from the invention and it is desired to cover all modifications falling within the spirit and scope of this invention.

What l claim as new and desire to secure by Letters Patent of the United States is:

1. A method for controlling the percentages by weight of at least a first and a second gas in a mixture, comprising the steps of:

a. separating said first gas into preset first and second parts;

b. mixing said first part of said first gas with said second gas;

c. comparing said second part of said first gas with the mixture of said first part of said first gas and said second gas as a function of their respective molecular weights and independently of their temperature;

d. varying the percentage of said second gas within the mixture of said second gas and said first part of said first gas to its desired value by weight in response to the comparison of said second part of said first gas with the mixture of said first part of said first gas and said second gas; and

e. mixing said second part of said first gas with the varied percentage by weight of said first part of said first gas and said second gas to obtain the controlled mixture of said first and second gases.

2. A method according to claim 1, wherein said comparing step is further comprised of the step of passing said second part of said first gas and the mixture of said first part of said first gas and said second gas through a heat exchanger to equalize the temperature between said second part of said first gas and the mixture of said first part of said first gas and said second gas.

3. A method according to claim 2, wherein the temperature of said first and second gases are constant and subsequent to passing the constituents of said first and second gases said comparing step is further comprised of the steps of:

a. converting said second part of said first gas to a first signal at a first frequency which is proportional to the molecular weight of said second part of said first gas;

b. converting the mixture of said first part of said first gas and said second gas to a second signal at a second frequency which is proportional to the molecular weight of the mixture of said first part of said first gas and said second gas;

0. detecting the difference between said first frequency and said second frequency of said respective first and second signals;

d. converting the detected difference frequency to an analog signal proportional to said difference frequency; and

e. comparing said analog signal with a reference signal to produce a control signal for controlling the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas.

4. A method according to claim 2, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing step is further comprised of the steps of:

a. generating a first signal at a first frequency proportional to the molecular weight of said second part of said first gas;

b. generating a second signal at a second frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas, the frequencies of said respective first and second signals being equal at the desired percentages by weight of said first and second gases in the mixture;

c. converting said first signal to a first analog signal proportional to said first frequency;

(1. converting said second signal to a second analog signal proportional to said second frequency; and

e. comparing said first and second analog signals to produce a change in a control signal only when adjustment in the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas is required.

5. A method according to claim 2, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing step further comprises the steps of:

a. generating first and second fluidic signals at a first frequency proportional to the molecular weight of said second part of said first gas, said first signal being 180 out of phase with said second signal;

b. feeding the mixture of said first part of said first gas and said second gas into a variable volume resonator cavity, the resonant frequency of said resonator cavity being proportional to the molecular weight of the mixture of said first part of said first gas and said second gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values;

r delaying the phase of said first generated signal by passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and

e. comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said first and second generated signals are unequal to the resonant frequency of said resonator cavity.

6. A method according to claim 2, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing step further comprises the steps of:

a. generating first and second fluidic signals at a first frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas, said first signal being 180 out of phase with said second signal;

b. feeding said second part of said first gas into a variable volume resonator cavity, the resonant frequency of said resonator cavity being proportional to the molecular weight of said second part of said first gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values;

c. delaying the phase of said first generated signal by d. passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and

e. comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said first and second generated signals are unequal to the resonent frequency of said resonator cavity;

7. An apparatus for controlling the percentages by weight of at least a first and a second gas in a mixture, comprising:

a. means for separating said first gas into preset first and second parts;

b. means for mixing said first part of said first gas with said second gas;

c. means for comparing said second part of said first gas with the mixture of said first part of said first gas and said second gas as a function of their respective molecular weights and independently of their temperature;

d. means for varying the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas to its desired value in response to the comparison of said second part of said first gas with the mixture of said first part of said first gas and said second gas; and

e. means for mixing said second part of said first gas with the varied percentage by weight of said first part of said first gas and said second gas to obtain the controlled mixture of said first and second gases.

8I An apparatus for controlling the percentages by weight of at least a first and a second gas in a mixture according to claim 7, wherein said comparing means is further comprised of a heat exchanger for equalizing the temperature between said second part of said first gas and the mixture of said first part of said first gas and said second gas as the gaseous constituents are received from said separating means and pass through said heat exchanger.

9. An apparatus for controlling the percentages by weight of at least a first and a second gas in a mixture according to claim 8, wherein the temperature of said first and second gases are constant, and subsequent to passing the constituents of said first and second gases through said heat exchanger, said comparing means is further comprised of:

a. means coupled to said heat exchanger for converting said second part of said first gas to a first signal at a first frequency which is proportional to the molecular weight of the second part of said first gas;

b. means coupled to said heat exchanger for converting the mixture of said first part of said first gas and said second gas to a second signal at a second frequency which is proportional to the molecular weight of the mixture of said first part of said first gas and said second gas;

c. means for detecting the differenc between said first frequency and said second frequency of said respective first and second signals;

d. means for converting the detected difference frequency to an analog signal proportional to said difference frequency; and

e. means for comparing said analog signal with a reference signal to produce a control signal for controlling the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas.

10. An apparatus for controlling the percentages by weight of a first and a second gas in a mixture according to claim 8, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger. said comparing means is further comprised of:

a. means coupled to said heat exchanger for generating a first signal at a first frequency proportional to the molecular weight of said second part of said first gas;

b. means coupled to said heat exchanger for generating a second signal at a second frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas, the frequencies of said respective first and second signals being equal at the desired percentages be weight of said first and second gases in the mixture;

c. means for converting said first signal to a first analog signal proportional to said first frequency;

d. means for converting said second signal to a second analog signal proportional to said second frequency; and

e. means for comparing said first and second analog signals to produce a change in a control signal only when adjustment in the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas is required.

11. An apparatus for controlling the percentages by weight of a first and a second gas in a mixture according to claim 8, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing means further comprises:

a. means coupled to said heat exchanger for generating first and second signals at a first frequency proportional to the molecular weight of said second part of said first gas, said first signal being 180 out of phase with said second signal;

b. a variable volume resonator cavity for receiving the mixture of said first part of said first gas and said second gas from said heat exchanger, the resonant frequency of said resonator cavity being proportional to the molecular weight of the mixture of said first part of said first gas and said second gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values;

0. means coupled to said generating means for delaying the phase of said first generated signal by 90;

d. means coupled to said generating means for passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and

e. a phase discriminator for comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said first and second generated signals are unequal to the resonant frequency of said resonator cavity.

l2. An apparatus for controlling the percentages by weight of a first and a second gas in a mixture according to claim 8, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing means further comprises:

a. means coupled to said heat exchanger for generating first and second signals at a first frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas,

said first signal being 180 out of phase with said v second signal;

b. a variable volume resonator cavity for receiving said second part of said first gas from said heat exchanger, the resonant frequency of said resonator cavity being proportional to the molecular weight of said second part of said first gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values;

c. means coupled to said generating means for delaying the phase of said first generated signal by d. means coupled to said generating means for passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and

. a phase discriminator for comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said first and second generated signals are unequal to the resonantfrequency of said resonator cavity.

13. A carburetor for controlling the fuel to air ratio by weight of a mixture of vaporized fuel and air to be fed into an internal combustion engine, comprising:

a. first and second flow paths for separating the air into first and second parts by weight;

b. means for feeding the vaporized fuel into said first flow path to mix the first part of the air with vaporized fuel;

c. a heat exchanger for equalizing the temperature of a representative portion by volume of the second part of the air with a representative portion by weight of the mixture of the first part of the air and the vaporized fuel;

d. a variable volume resonator cavity for receiving from said heat exchanger the representative portion of the mixture of the first part of the air and the vaporized fuel, said resonator cavity having a resonant frequency proportional to the molecular weight of the mixture of the first part of the air and the vaporized fuel and to the volume of said resonator cavity;

e. means coupled to the output of said heat exchanger for generating first and second fluidic signals at a first frequency proportional to the molecular weight of the representative portion of the second part of the air, the respective first and second generated signals being 180 out of phase with one another;

f. means for delaying the phase of the first generated signal by 90;

g. means for passing the second generated signal through and out of said resonator cavity to shift the phase of the second generated signal only when the frequency of the second generated signal is unequal to the resonant frequency of said resonator cavity; and

h. a phase discriminator for comparing the delayed first generated signal with the second generated signal after the second generated signal has passed through said resonator cavity to produce a control signal for adjusting the feed of the vaporized fuel into said first flow path only when the frequency of the second generated signal is unequal to the resonant frequency of said resonator cavity to thereby obtain the desired fuel to air ratio by weight for the gaseous mixture to be fed to the internal combustion engine.

14. A carburetor for controlling the fuel to air ratio by weight of a mixture of vaporized fuel and air which is to be fed to an internal combustion engine, comprismg:

a. first and second flow paths for separating the air into first and second parts by weight;

b. means for feeding vaporized fuel into said first flow path to mix the first part of the air with the vaporized fuel;

c. a heat exchanger for equalizing the temperature of a representative portion by weight of the second part of the air with a representative portion by weight of the mixture of the first part of the air and the vaporized fuel;

d. a variable volume resonator cavity for receiving from said heat exchanger the representative portion of the second part of the air, said resonator cavity having a resonant frequency proportional to the molecular weight of the second part of the air and the volume of said resonator cavity;

. means coupled to the output of said heat exchanger for generating first and second fluidic signals at a first frequencyoproportional to the molecular weight of the representative portion of the first part of the air and the vaporized fuel, the respective first and second generated signals being 180 out of phase with one another;

f. means for delaying the phase of the first generated signal by g. means for passing the second generated signal through and out of said resonator cavity to shift the phase of the second generated signal only when the frequency of the second generated signal is unequal to the resonant frequency of said resonator cavity; and

h. a phase discriminator for comparing the delayed 2 2g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,844,304 Dated October 29, 1974 Inventor(s) Willis A. Boothe It is certified that error appears in the above-identified-patent and that said Letters Patent are hereby corrected as shown below:

ClaimlO, line 16, after "percentages" delete be" and insert by Claim 13, line 7, after "air with" insert the (SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Commissioner of Patents Attesting Officer 

1. A method for controlling the percentages by weight of at least a first and a second gas in a mixture, comprising the steps of: a. separating said first gas into preset first and second parts; b. mixing said first part of said first gas with said second gas; c. comparing said second part of said first gas with the mixture of said first part of said first gas and said second gas as a function of their respective molecular weights and independently of their temperature; d. varying the percentage of said second gas within the mixture of said second gas and said first part of said first gas to its desired value by weight in response to the comparison of said second part of said first gas with the mixture of said first part of said first gas and said second gas; and e. mixing said second part of said first gas with the varied percentage by weight of said first part of said first gas and said second gas to obtain the controlled mixture of said first and second gases.
 2. A method according to claim 1, wherein said comparing step is further comprised of the step of passing said second part of said first gas and the mixture of said first part of said first gas and said second gas through a heat exchanger to equalize the temperature between said second part of said first gas and the mixture of said first part of said first gas and said second gas.
 3. A method according to claim 2, wherein the temperature of said first and second gases are constant and subsequent to passing the constituents of said first and second gases said comparing step is further comprised of the steps of: a. converting said second part of said first gas to a first signal at a first frequency which is proportional to the molecular weight of said second part of said first gas; b. converting the mixture of said first part of said first gas and said second gas to a second signal at a second frequency which is proportional to the molecular weight of the mixture of said first part of said first gas and said second gas; c. detecting the difference between said first frequency and said second frequency of said respective first and second signals; d. converting the detected difference frequency to an analog signal proportional to said difference frequency; and e. comparing said analog signal with a reference signal to produce a control signal for controlling the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas.
 4. A method according to claim 2, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing step is further comprised of the steps of: a. generating a first signal at a first frequency proportional to the molecular weight of said second part of said first gas; b. generating a second signal at a second frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas, the frequencies oF said respective first and second signals being equal at the desired percentages by weight of said first and second gases in the mixture; c. converting said first signal to a first analog signal proportional to said first frequency; d. converting said second signal to a second analog signal proportional to said second frequency; and e. comparing said first and second analog signals to produce a change in a control signal only when adjustment in the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas is required.
 5. A method according to claim 2, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing step further comprises the steps of: a. generating first and second fluidic signals at a first frequency proportional to the molecular weight of said second part of said first gas, said first signal being 180* out of phase with said second signal; b. feeding the mixture of said first part of said first gas and said second gas into a variable volume resonator cavity, the resonant frequency of said resonator cavity being proportional to the molecular weight of the mixture of said first part of said first gas and said second gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values; c. delaying the phase of said first generated signal by 90*; d. passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and e. comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said first and second generated signals are unequal to the resonant frequency of said resonator cavity.
 6. A method according to claim 2, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing step further comprises the steps of: a. generating first and second fluidic signals at a first frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas, said first signal being 180* out of phase with said second signal; b. feeding said second part of said first gas into a variable volume resonator cavity, the resonant frequency of said resonator cavity being proportional to the molecular weight of said second part of said first gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values; c. delaying the phase of said first generated signal by 90*; d. passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and e. comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said first and second generated signals are unequal to the rEsonent frequency of said resonator cavity.
 7. An apparatus for controlling the percentages by weight of at least a first and a second gas in a mixture, comprising: a. means for separating said first gas into preset first and second parts; b. means for mixing said first part of said first gas with said second gas; c. means for comparing said second part of said first gas with the mixture of said first part of said first gas and said second gas as a function of their respective molecular weights and independently of their temperature; d. means for varying the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas to its desired value in response to the comparison of said second part of said first gas with the mixture of said first part of said first gas and said second gas; and e. means for mixing said second part of said first gas with the varied percentage by weight of said first part of said first gas and said second gas to obtain the controlled mixture of said first and second gases.
 8. An apparatus for controlling the percentages by weight of at least a first and a second gas in a mixture according to claim 7, wherein said comparing means is further comprised of a heat exchanger for equalizing the temperature between said second part of said first gas and the mixture of said first part of said first gas and said second gas as the gaseous constituents are received from said separating means and pass through said heat exchanger.
 9. An apparatus for controlling the percentages by weight of at least a first and a second gas in a mixture according to claim 8, wherein the temperature of said first and second gases are constant, and subsequent to passing the constituents of said first and second gases through said heat exchanger, said comparing means is further comprised of: a. means coupled to said heat exchanger for converting said second part of said first gas to a first signal at a first frequency which is proportional to the molecular weight of the second part of said first gas; b. means coupled to said heat exchanger for converting the mixture of said first part of said first gas and said second gas to a second signal at a second frequency which is proportional to the molecular weight of the mixture of said first part of said first gas and said second gas; c. means for detecting the differenc between said first frequency and said second frequency of said respective first and second signals; d. means for converting the detected difference frequency to an analog signal proportional to said difference frequency; and e. means for comparing said analog signal with a reference signal to produce a control signal for controlling the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas.
 10. An apparatus for controlling the percentages by weight of a first and a second gas in a mixture according to claim 8, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing means is further comprised of: a. means coupled to said heat exchanger for generating a first signal at a first frequency proportional to the molecular weight of said second part of said first gas; b. means coupled to said heat exchanger for generating a second signal at a second frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas, the frequencies of said respective first and second signals being equal at the desired percentages be weight of said first and second gases in the mixture; c. means for converting said first signal to a first analog signal proportional to said first frequency; d. means for converting said second signal to a second analog signal proportional to said second frequency; and e. means for comparing said first and second analog signals to produce a change in a contrOl signal only when adjustment in the percentage by weight of said second gas within the mixture of said second gas and said first part of said first gas is required.
 11. An apparatus for controlling the percentages by weight of a first and a second gas in a mixture according to claim 8, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing means further comprises: a. means coupled to said heat exchanger for generating first and second signals at a first frequency proportional to the molecular weight of said second part of said first gas, said first signal being 180* out of phase with said second signal; b. a variable volume resonator cavity for receiving the mixture of said first part of said first gas and said second gas from said heat exchanger, the resonant frequency of said resonator cavity being proportional to the molecular weight of the mixture of said first part of said first gas and said second gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values; c. means coupled to said generating means for delaying the phase of said first generated signal by 90*; d. means coupled to said generating means for passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and e. a phase discriminator for comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said first and second generated signals are unequal to the resonant frequency of said resonator cavity.
 12. An apparatus for controlling the percentages by weight of a first and a second gas in a mixture according to claim 8, wherein subsequent to the passing of the constituents of said first and second gases through said heat exchanger, said comparing means further comprises: a. means coupled to said heat exchanger for generating first and second signals at a first frequency proportional to the molecular weight of the mixture of said first part of said first gas and said second gas, said first signal being 180* out of phase with said second signal; b. a variable volume resonator cavity for receiving said second part of said first gas from said heat exchanger, the resonant frequency of said resonator cavity being proportional to the molecular weight of said second part of said first gas and the volume of said resonator cavity, the resonant frequency of said resonator cavity being equal to the frequency of said first and second generated signals when the percentages by weight of said first and second gases are at their desired values; c. means coupled to said generating means for delaying the phase of said first generated signal by 90*; d. means coupled to said generating means for passing said second generated signal through and out of said resonator cavity to shift the phase of said second generated signal only when the frequency of said second generated signal is unequal to the resonant frequency of said resonator cavity; and e. a phase discriminator for comparing the phase of the delayed first generated signal with the phase of said second generated signal after said second generated signal has passed through said resonator cavity to produce an output signal for controlling the adjustment of the percentage by weight of said second gas within said first part of said first gas when the frequency of said firsT and second generated signals are unequal to the resonant frequency of said resonator cavity.
 13. A carburetor for controlling the fuel to air ratio by weight of a mixture of vaporized fuel and air to be fed into an internal combustion engine, comprising: a. first and second flow paths for separating the air into first and second parts by weight; b. means for feeding the vaporized fuel into said first flow path to mix the first part of the air with vaporized fuel; c. a heat exchanger for equalizing the temperature of a representative portion by volume of the second part of the air with a representative portion by weight of the mixture of the first part of the air and the vaporized fuel; d. a variable volume resonator cavity for receiving from said heat exchanger the representative portion of the mixture of the first part of the air and the vaporized fuel, said resonator cavity having a resonant frequency proportional to the molecular weight of the mixture of the first part of the air and the vaporized fuel and to the volume of said resonator cavity; e. means coupled to the output of said heat exchanger for generating first and second fluidic signals at a first frequency proportional to the molecular weight of the representative portion of the second part of the air, the respective first and second generated signals being 180* out of phase with one another; f. means for delaying the phase of the first generated signal by 90*; g. means for passing the second generated signal through and out of said resonator cavity to shift the phase of the second generated signal only when the frequency of the second generated signal is unequal to the resonant frequency of said resonator cavity; and h. a phase discriminator for comparing the delayed first generated signal with the second generated signal after the second generated signal has passed through said resonator cavity to produce a control signal for adjusting the feed of the vaporized fuel into said first flow path only when the frequency of the second generated signal is unequal to the resonant frequency of said resonator cavity to thereby obtain the desired fuel to air ratio by weight for the gaseous mixture to be fed to the internal combustion engine.
 14. A carburetor for controlling the fuel to air ratio by weight of a mixture of vaporized fuel and air which is to be fed to an internal combustion engine, comprising: a. first and second flow paths for separating the air into first and second parts by weight; b. means for feeding vaporized fuel into said first flow path to mix the first part of the air with the vaporized fuel; c. a heat exchanger for equalizing the temperature of a representative portion by weight of the second part of the air with a representative portion by weight of the mixture of the first part of the air and the vaporized fuel; d. a variable volume resonator cavity for receiving from said heat exchanger the representative portion of the second part of the air, said resonator cavity having a resonant frequency proportional to the molecular weight of the second part of the air and the volume of said resonator cavity; e. means coupled to the output of said heat exchanger for generating first and second fluidic signals at a first frequency proportional to the molecular weight of the representative portion of the first part of the air and the vaporized fuel, the respective first and second generated signals being 180* out of phase with one another; f. means for delaying the phase of the first generated signal by 90*; g. means for passing the second generated signal through and out of said resonator cavity to shift the phase of the second generated signal only when the frequency of the second generated signal is unequal to the resonant frequency of said resonator cavity; and h. a phase discriminator for comparing the delayed first generated signal with the second generated signal after the second generaTed signal has passed through said resonator cavity to produce a control signal for adjusting the feed of the vaporized fuel into said first flow path only when the frequency of the second generated signal is unequal to the resonant frequency of said resonator cavity to thereby obtain the desired fuel to air ratio for the gaseous mixture to be fed to the internal combustion engine. 